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studeclunker
05-01-2005, 04:36 PM
I have a 64 Commander wagon with front disc brakes.[8D] The outside piston isn't retracting to allow free movement. I.E. it drags.:( Both sides do this. If it was one side, I would think there is a defect in the brake. As it is, being that both sides are affected the same, could it be the master cylinder?

I'm stumped.[:o)] Everything looks right. It just won't completely back off. I replaced the single M.C. with a double M.C. a few weeks ago and thoroughly bled the system.[:I] Could this be the problem? Should I go back to the single?

Thanks in advance!

Lotsa Larks!
Studeclunker
A.K.A: out2lunch

Roscomacaw
05-01-2005, 05:09 PM
Uhhhhh... did you remove the residual pressure valve from the part of the dual MC that serves the front brakes?[?] If not - that's your problem![:0]

Miscreant at large.

Mike
05-01-2005, 05:11 PM
Master cylinders for use with drum brakes usually have a residual pressure valve, which keeps about 3 to 5 pounds of pressure in the lines with the brakes released. The "RPV" is a small, spring loaded, one way valve. You can't use this feature, with disc brakes since there is no return spring at the brake. On the tandem cylinder I used, the rear section has no RPV, and the front section does. I connect the front discs to the rear section. The small pressure in the front section, connected to the rear drums, keeps seals in place and prevents rattles.
Your new master could have one, two, or no RPV'S.
It's also possible the push rod length isn't adjusted to let the master release fully. There should be a very slight amount of free play.
Mike M.

studeclunker
05-02-2005, 01:03 AM
Okayyyyy... So this RPV keeps a little pressure in the lines...

1. Where is the RPV? ie: where do I find it in the master cylinder.

2. How do I remove it?

3. Why is it that only one side (the outer) of the brake is in contact and the inner moves out?

Do I sound rather ignorant?[8)] Why yes, I am actually.[V] Ask me where to plug in a CD ROM drive and I can do it in seconds. Ask me where the CPU is in a computer and I can locate it just as quickly. Ask me where the RPV is in the master cylinder and you will get the dial tone: DUHHHHHHHHHHHH....[:o)]

I'm still learning...[:o)] Have patience with me please.[:I]
Thanks in advance. You guys are really worth your weight in gold.:D



Lotsa Larks!
Studeclunker
A.K.A: out2lunch

Roscomacaw
05-02-2005, 12:27 PM
The valve is a little rubber/metal thingy that sits in the outlet port(s) of the MC.

BTW, the rear (drum) brakes of a stock Stude setup are engineered in such a way as to not need residual pressure. That's how they got away with using a single MC instead of a dual.;) So if you're still using the original rear drum brakes, you need to disable both residual valves in that dual MC.
;)

Backing up a bit..... What degree of "drag" is it you're worried about??[?] I ask that because disc brakes can touch the surface ever so slightly after application. The way they're return springs are set up, there's not much backing off of the pads after application. Have you seen inside the caliper bores? Maybe they're grungy? Maybe the return springs are on the hooey?
[B)]

This consideration is maybe drastic - but not totally unbelieveable - if the calipers were reinstalled without aligning them with the rotor - ala shim washers - maybe there's NO shims between the calipers and the bracket they mount up to. If that was the case, I could see the outer piston bottomed in it's bore and jammed against the rotor while the inner one would have room to move.[:0]

No problem with the "learning curve"[}:)] I'm still learnin', myself.[xx(] Next time this computerclunker locks up it's brakes, I'll know who to call on!:D

Miscreant at large.

studeclunker
05-02-2005, 12:50 PM
My other cars wheels spin freely when jacked off the ground. These do not. I can move them with little effort, they do not, however move freely. I wouldn't know about shims and so on. The brakes themselves haven't been touched yet. Looked at yes, not modified. I just changed out the single MC with a double.

Oh-kayyyy... To get to this valve you have been speaking of... I just disconnect the brake lines and fish around???



Lotsa Larks!
Studeclunker
A.K.A: out2lunch

Mike
05-02-2005, 01:33 PM
The RPV can be in the master cylinder bore or built into a fitting. You should be able to see that the fluid is under a little pressure by opening a bleeder valve, or loosening a line on the master. If the master you are using was intended for all discs you won't have an RPV. If it was disc/drum, only one side will have it; and you need to hook the lines up accordingly. Mine was made for a 70's Chrysler. The rear section is connected to the discs. What car was your master cylinder made for?
The single master Stude used with front disc brakes didn't have an RPV or any provision to keep pressure in the rear lines. One of the advantages of a tandem cylinder is that you can. It helps keep the cylinder cups in position.
If there is pressure from the master, the pads on both sides of the disc should be dragging.
Was everything OK before you changed the master?
There isn't anything Stude calls a return spring on the front discs. In use, bearing play, disc run out, and parts flexing moves the pads away from the disc; and the "retainer" keeps them there. It's common disc brake design. Some other manufacturers do call parts like the "retainer", a return spring. It's misleading.
Mike M.

Roscomacaw
05-02-2005, 05:21 PM
Mike,
I assume you have the late Stude car shop manual at your disposal. Flip to the subsection called group One - then to page 48 of that section. Thereupon, read the "Principles of Operation" regarding the front disc brakes. Also note the cutaway view of a Bendix caliper on the bottom right corner of the page. One of the items pointed out in that view is labelled a "retractor spring". What would it's function be if not to retract the puck and pad after an application of the brakes[?]

Might I quote the text: " As hydraulic pressure is released from the wheel cylinders, the pressure that was applied to the retracting mechanisim spring will assist in retracting the wheel cylinder piston and friction pads. The retracting mechanisim connects the wheel cylinder piston, through a spring, a spring seat, and a friction type bushing to a stationary spring that is secured to the wheel cylinder body."

Having noted all this, I agree that MOST disc brakes that I've seen do not have a "return (or retraction) spring incorporated. But these Bendix/Dunlop do.;)

Miscreant at large.

studeclunker
05-02-2005, 09:37 PM
Ok. The master cylinder came out of my other '64 wagon. It was procured for me by a mechanic in Riverside CA before I moved up here. No it wasn't made specifically for Studebaker. That said, it is visibly at least,identical to the one it replaced.[:I] The wagon it came out of had drum brakes all round. The brakes on the other wagon worked perfectly. The mechanic that did the job for me was trained in the Studebaker dealership in Riverside. He used to really get a kick out of my car.;)

All that said... Where do I find these RPVs again?[:o)] Forgive me please, it's just that I don't want to screw up the brakes of all things...[:I] You see, I live on the side of a mountain. Brakes are kind of important. Ya know? I don't want to end up in the third forum mentioned here....[xx(]

Lotsa Larks!
Studeclunker
A.K.A: out2lunch

Mike
05-03-2005, 07:54 AM
I suggest you check for pressure in the line to the front brakes, at the master:
Apply the brakes. Release them. Loosen the line at the master. Does fluid ooze or is there pressure at first? Compare to the other line at the master.
If you have to remove an RPV, it may be inside the cylinder or incorporated in the fitting. Try to find a parts drawing of a cylinder like yours. Stude just called the RPV a "valve" on the drawings of single cylinders. It was inside the bore, at the outlet. It may be called a "check valve".
I had forgotten about all the little goodies inside the wheel cylinders, and the manufacturers claim that they retract, and are self adjusting, too. The retracting effect is claimed to merely "assist" in moving the pad away from the disc. It isn't even enough to overcome residual pressure, which is insufficient to activate the brake lites!
The description of operation, should read: "The retracting mechanism connects ... to a stationary pin that is secured to the wheel cylinder body." That's how it is in the Avanti manual. It's probably paraphrased from Dunlop's description. I gather Stude got it wrong in some manuals. All the springs are in the piston. There is no "stationary spring that is secured to the wheel cylinder body".
Mike M.

Roscomacaw
05-03-2005, 08:50 AM
The residual pressure valves in the late Stude dual master cylinder are right in the outlets of the master cylinder. Right where the lines plug in. OF COURSE - even tho you assured us that this later, non-Stude dual MC "looks just like the original Stude MC", there's no GUARANTEE that it's identical INSIDE.

Clunker - you've yet to tell us if these brakes worked fine BEFORE this MC was installed[}:)] In other words - was the MC the ONLY thing messed with before this problem arose? Did you even so much as install new pads in the calipers?

You said: "My other cars wheels spin freely when jacked off the ground. These do not. I can move them with little effort, they do not, however move freely. I wouldn't know about shims and so on. The brakes themselves haven't been touched yet. Looked at yes, not modified. I just changed out the single MC with a double."

So have you actualy driven this car before the MC swap? I don't mean 20 feet or so, down the driveway - I mean out on the open road.[:I]
The point I'm making is that if someone had worked on the brakes BEFORE you aquired the car - and had neglected to reinstall the shim washers, I could - as I mentioned previously - see the outer calipers jammed, while the inner ones float free.
These Bendix calipers required more than a simple wrench and matching grease monkey to remove and replace (as is the case with today's disc brakes). The shims were/are a very important consideration when reinstalling the calipers after them having been worked on. Reinstalling them means trial and error fitment - adding or subtracting shims until you get the caliper centered with respect to the rotor. I could EASILY see a "know-not" "mechanic" installing the calipers and dismissing or not even being aware of the shims. My experience is that it takes a fair (and equal) number of them on each attaching bolt to get proper alignment.:)
Try this and see what happens: Jack up the front of the car and confirm that the brakes are dragging, as you say.
Then crack loose the pertinent brake line fitting at the MC so that you KNOW pressure is gone in that part of the system.
Now go back and check to see if the brakes still drag the same or are now able to spin freely. If they DO - dig out the RPVs - if they STILL drag (and only on the outside pads), you've got problems with the calipers themselves OR their alignment.;)
Try the loose-line test and answer my questions here. Then we'll go from there.[^]

Miscreant at large.

studeclunker
05-04-2005, 02:44 PM
Ok... Here we go on the questions:

1.) The car is my daily driver.[:I] It has been for about a year.
It had a power booster and single MC originally. I replaced
the original because the booster failed.:( I was told that
a double MC would'nt work with the booster so I did'nt replace
that part.

2.) Yes I drove the car quite a lot before the swap. If I could have kept the booster I would have. I like power brakes. These PB were especially nice.[8D]

3.) Fluid drips out. After working the wheel back and forth a bit it is free-er moving. Though I can't say it is completely free spinning. My '62 sedan (drum) wheels spin quite freely, in comparison these don't. One more note on this... When I have driven any distance, ie; work, the wheels are cool. That is to say, things don't heat up.

Oh yes and I do have the shop manual, Chassis and body books.

Thanks again for all your time.

Lotsa Larks!
Studeclunker
A.K.A: out2lunch

Roscomacaw
05-04-2005, 02:46 PM
OK, that's all fine, but you still didn't tell me if YOU had taken the front calipers off and reinstalled them with attention to alignment using the aforementioned shims. have you had them off? Have you replaced the pads of late[?]

Miscreant at large.

studeclunker
05-04-2005, 02:47 PM
Sorry, Thought I was clear on that. [:I] No I haven't touched the brake pads, shims or calipers. The only thing I have done is replace the master cylinder. I also changed the system from a single to double system. That's it.[8)]

I have checked the pads (visually without taking anything apart) and they look fine. Then again, what's fine with these? I'm used to motorcycles and Cadillacs. Looks to me like there's 1/2"-3/8" of material on them. Seems ok to me. My philosophy is to leave well enough alone. So in regards to that part of the system I did.

What the previous owner had or had not done I don't know. I suppose I should ask. Still, they were fine till I changed the master cylinder.

Lotsa Larks!
Studeclunker
A.K.A: out2lunch

Roscomacaw
05-06-2005, 01:06 PM
OK - so they "worked" fine with the old MC - but don't work "fine" with the new, different, MC. See if there ARE RPVs in that dual MC, remove them, then come back and tell us the results.:D
Yes, I'm stumped that only the outside pads are dragging as common sense would tell you that pressure should be equal on all four pistons. [|)]
Are/were the pads wearing evenly before this[?]

Miscreant at large.

studeclunker
05-07-2005, 02:49 AM
Yes the pads were wearing evenly. They seem to be still doing so. The brakes work fine. It's just the front drag. Go figure...[:I]
It's going to be a few days before I can get to this. The car is broken down in Redding, thirty miles away.:( The soonest I can get it home is Monday. Sigh... The yoke came out of the rear end.:(

There's a reason I call er the blue witch.[V]

Lotsa Larks!
Studeclunker
A.K.A: out2lunch